outputting unique titles and partial sums

I have been trying to get the following output

{month}:{sum of spots for that month} {month}:{sum of spots for that month}

Can someone help me spot what's not working on my code?

Here is the xml doc:
				<prop_tv_station>
					<prop_tv_program>
						<air_month>
	
<month_name>September</month_name>
	
<num_spots>12</num_spots>
						</air_month>
						<air_month>
	
<month_name>January</month_name>
	
<num_spots>12</num_spots>
						</air_month>
					</prop_tv_program>
				</prop_tv_station>

There are multiple tv programs each with a set of air_month. And I want to
get a list of unique months and the sum of num_spots for these months.  Here
is my code:


  <xsl:variable name="month-list" 
            select="//month_name[not(.=following::month_name) and
not(.='')]" />
	
	  <xsl:variable name="monthsum">
		  <xsl:for-each select="$month-list"> 
		    <xsl:variable name="monthname" select="."/>
		      <xsl:value-of select="$monthname"/>
		      <xsl:text>:</xsl:text>
		      <xsl:value-of
select="//air_month[month_name=$monthname]/num_spots"/>
		      <xsl:text>&#xa;</xsl:text>
		  </xsl:for-each>
	  </xsl:variable>

		
	   <TR bgcolor="#FFFF99">
		   <TD valign="middle" CLASS="cne_programs_item"
colspan="9"><xsl:text> Subtotals: </xsl:text>
   			<!--<xsl:value-of
select="count($month-list)"/><xsl:text> programs.  </xsl:text>-->
   			<xsl:value-of select="$monthsum"/>
		   </TD>   
	   </TR> 

Thanks in advance for any help!

Amy

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